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A195613 Numbers n with property that n, 2n-1 and 2n+1 are composite. 0
25, 28, 32, 38, 46, 58, 60, 62, 72, 77, 80, 85, 88, 92, 93, 94, 102, 104, 108, 110, 118, 122, 123, 124, 130, 133, 143, 144, 145, 148, 150, 152, 160, 161, 162, 164, 170, 171, 172, 178, 182, 185, 188, 196, 202, 203, 206, 207, 208, 212, 213, 214, 218, 226, 235 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

In A000027, if n, n+(n-1) and n+(n+1) are composite, then n is a term of this sequence.

Suggestion: there are arbitrarily long sets of consecutive integers, e.g., 632..637, 665..672, 6428..6443.

LINKS

Table of n, a(n) for n=1..55.

MATHEMATICA

Select[Range[2, 1000], !PrimeQ[2#-1]&&!PrimeQ[#]&&!PrimeQ[2#+1]&]

CROSSREFS

Sequence in context: A221617 A083806 A239521 * A127652 A234640 A219258

Adjacent sequences:  A195610 A195611 A195612 * A195614 A195615 A195616

KEYWORD

nonn

AUTHOR

Zak Seidov, Sep 21 2011

STATUS

approved

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Last modified November 28 11:56 EST 2014. Contains 250348 sequences.